Systems and methods for quick dissipation of stored energy from input capacitors of power inverters

ABSTRACT

Methods and systems for connecting a photovoltaic module and an inverter having an input capacitor are presented. The photovoltaic system includes a maximum power point tracking (MPPT) controller coupled between the inverter and the photovoltaic module. The MPPT controller includes a direct current (DC) converter configured to reduce, in a forward buck mode, a voltage of the photovoltaic module, to supply power from the photovoltaic module to the input capacitor of the inverter. The photovoltaic system also includes a microcontroller unit (MCU) configured to control the DC converter to allow the photovoltaic module to operate at a maximum power point, and to increase, in a reverse boost mode, a voltage of the input capacitor of the inverter, to dissipate power from the input capacitor in the photovoltaic module, and the MPPT controller is configured to, based upon one or more triggers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 16/841,408, filed Apr. 6, 2020, which is acontinuation application of U.S. patent application Ser. No. 15/159,699,filed May 19, 2016, entitled “Systems and Methods for Quick Dissipationof Stored Energy from Input Capacitors of Power Inverters”, which claimsthe benefit of the filing date of Provisional U.S. Pat. App. Ser. No.62/165,672, filed May 22, 2015, entitled “Systems and Methods for QuickDissipation of Stored Energy from Input Capacitors of Power Invertersduring Emergency Shutdown of Photovoltaic Systems”, the entiredisclosures of which applications are hereby incorporated herein byreference.

The present application relates to U.S. Pat. Pub. No. 2014/0327313,filed Apr. 23, 2014 and entitled “System and Method for Low-Cost,High-Efficiency Solar Panel Power Feed,” which claims the benefit of thefiling date of Provisional U.S. Patent Application Ser. No. 61/818,036,filed May 1, 2013 and entitled “System and Method for Low-Cost,High-Efficiency Solar Panel Power Feed,” the disclosures of whichapplications are incorporated herein by reference. The presentapplication further relates to U.S. Patent Application Publication No.2013/0026840, filed on Jan. 9, 2012 and entitled “Systems and Methods toReduce the Number and Cost of Management Units of Distributed PowerGenerators,” and U.S. Pat. No. 8,314,375, issued on Nov. 20, 2012 andentitled “System and Method for Local String Management Unit,” theentire disclosures of which applications or patents are herebyincorporated herein by reference.

BACKGROUND Field of the Disclosure

The present disclosure is related to photovoltaic systems in general,and more particularly to the safety-enhancing modules for quicklydischarging capacitors in photovoltaic systems.

Description of Related Art

Photovoltaic systems are becoming increasingly common for powergeneration. Photovoltaic systems are safe, clean sources of power, whichfunction reliably and last many years once installed. The use of thesesystems is only expected to grow in the future as the costs of thesesystems continues to decrease, and alternative energy resources areimplemented in the energy economy.

In a case of fire or other emergency, when any electrical powergeneration or distribution system must be shut down quickly, there areknown electrical hazards associated with electrical power generation anddistribution systems. Thus, safety systems form an important part ofelectrical power generation and distribution systems to account forthis, and there are methods and systems known for de-energizingtraditional electrical power systems during emergencies. However,photovoltaic systems present some unique difficulties, which are notadequately resolved by conventional safety systems.

BRIEF SUMMARY

One embodiment of the disclosure is drawn to a photovoltaic systemconnected to an inverter having an input capacitor. The photovoltaicsystem includes at least one photovoltaic module and a maximum powerpoint tracking (MPPT) controller coupled between the input capacitor ofthe inverter and the at least one photovoltaic module. The MPPTcontroller includes a direct current (DC) converter configured toreduce, in a forward buck mode, a voltage of the at least onephotovoltaic module, to supply power from the at least one photovoltaicmodule to the input capacitor of the inverter.

The photovoltaic system also includes a microcontroller unit (MCU)configured to control the DC converter to allow the at least onephotovoltaic module to operate at a maximum power point. The DCconverter is software-configurable to increase, in a reverse boost mode,a voltage of the input capacitor of the inverter, to dissipate powerfrom the input capacitor in the at least one photovoltaic module, andthe MPPT controller is configured to, based upon one or more triggers,automatically change the DC converter from the forward buck mode to thereverse boost mode to dissipate energy stored in the input capacitor ofthe inverter.

One embodiment of the disclosure is drawn to a system connecting atleast one photovoltaic module to an inverter having an input capacitor.The system includes a maximum power point tracking (MPPT) controllercoupled between the input capacitor of the inverter and the at least onephotovoltaic module. The MPPT controller includes a direct current (DC)converter configured to reduce, in a forward buck mode, a voltage of theat least one photovoltaic module, to supply power from the at least onephotovoltaic module to the input capacitor of the inverter.

The system also includes a microcontroller unit (MCU) configured tocontrol the DC converter to allow the at least one photovoltaic moduleto operate at a maximum power point. The DC converter issoftware-configurable to increase, in a reverse boost mode, a voltage ofthe input capacitor of the inverter, to dissipate power from the inputcapacitor in the at least one photovoltaic module, and the MPPTcontroller is configured to, based upon one or more triggers,automatically change the DC converter from the forward buck mode to thereverse boost mode to dissipate excess energy stored in the inputcapacitor.

One embodiment of the disclosure is drawn to a method for transferringenergy between at least one photovoltaic module and an inverter havingan input capacitor. The method includes coupling a maximum power pointtracking (MPPT) controller between the input capacitor of the inverterand the at least one photovoltaic module. The MPPT controller includes adirect current (DC) converter configured to reduce, in a forward buckmode, a voltage of the at least one photovoltaic module, to supply powerfrom the at least one photovoltaic module to the input capacitor of theinverter, and a microcontroller unit (MCU) configured to control the DCconverter to allow the at least one photovoltaic module to operate at amaximum power point. The DC converter is software-configurable toincrease, in a reverse boost mode, a voltage of the input capacitor ofthe inverter, to dissipate power from the input capacitor in the atleast one photovoltaic module.

The method also includes bucking, as controlled by the MCU, the voltageof the at least one photovoltaic module to the inverter via the DCconverter in the forward buck mode to supply power to the inputcapacitor of the inverter, monitoring, by the MCU, one or more triggersfor an emergency shutdown condition, and changing, as controlled by theMCU, upon a determination by the MCU from the monitoring that anemergency shutdown condition has been met, the DC converter from theforward buck mode to the reverse boost mode.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosed embodiments and many ofthe attendant advantages thereof will be more readily obtained byreference to the accompanying drawings when considered in connectionwith the following detailed description.

FIG. 1 is a schematic structural diagram illustrating photovoltaic cellsin a photovoltaic module according to some embodiments of the presentdisclosure.

FIG. 2 is a schematic structural diagram illustrating strings ofphotovoltaic modules in a photovoltaic array according to someembodiments of the present disclosure.

FIGS. 3A-3C are schematic structural diagrams illustrating differentinverter locations in photovoltaic arrays according to some non-limitingembodiments of the present disclosure.

FIGS. 4A and 4B are schematic structural diagrams illustrating a powerconverting system including a maximum power point tracking (MPPT)controller according to some embodiments of the present disclosure.

FIG. 5 is a schematic structural diagram illustrating a photovoltaicsystem including an MPPT controller according to some embodiments of thepresent disclosure.

FIG. 6 is a schematic structural diagram illustrating a photovoltaicsystem including an MPPT controller according to some embodiments of thepresent disclosure.

FIG. 7 is a schematic structural diagram illustrating a photovoltaicsystem including an MPPT controller according to some embodiments of thepresent disclosure.

FIG. 8 is a schematic flowchart illustrating a process for transferringenergy between at least one photovoltaic module and an inverter havingan input capacitor according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following descriptions are meant to further clarify the presentdisclosure by giving specific examples and embodiments. Theseembodiments are meant to be illustrative rather than exhaustive. Thefull scope of the disclosure is not limited to any particular embodimentdisclosed in this specification, but rather is defined by the dependentclaims.

In view of the above, a system and method that, in the case of anemergency shutdown, shuts down not only the panels, but also providesfor a safe and quick dissipation of the energy stored on the inputcapacitors of the inverter is needed. This renders the solar wiring safefor people to accidentally touch, without any bodily harm.

FIG. 1 is a schematic structural diagram illustrating photovoltaic cellsin a photovoltaic module according to some embodiments of the presentdisclosure.

A typical photovoltaic (PV) system includes photovoltaic cells 100, orsolar cells, which absorb light and convert the energy of the light intoelectricity via the photovoltaic effect. The PV cells 100 are connectedin series and/or in parallel in PV modules 102, or solar modules, inorder to produce a desired voltage and current. Solar modules 102 maythen also be connected in series and in parallel, using output terminals101 a and 101 b, according to the desired output characteristics of thePV system. A PV system tied to an electrical grid, for example, willtypically have different output requirements than a stand-alone PVsystem for charging a battery.

FIG. 2 is a schematic structural diagram illustrating strings ofphotovoltaic modules in a photovoltaic array according to someembodiments of the present disclosure.

Solar modules 102 a 1 through 102 mn are usually mounted on panels,which may each hold one or more solar modules. A group of solar modules102 a 1 through 102 an connected together is also called a string ofsolar modules. Strings of solar modules are usually wired in series viaa “string” or power bus 116 a through 116 m to produce a required outputvoltage. Strings which are too small will sacrifice efficiency; stringswhich are too large can damage other equipment in the PV system, such asinverters, void equipment warranties, or violate local electrical codes.APV array, or solar array, may contain multiple strings 116 a through116 m of solar modules 102 a 1 through 102 mn.

Solar modules 102 a 1 through 102 mn may be connected to the strings 116a through 116 m via local management units (LMUs) 104 a 1 through 104mn, respectively. The LMUs may also be referred to as solar modulecontrollers, solar module converters, or link module units. The LMUs maybe used to switch the solar modules 102 a 1 through 102 mn on and offperiodically to improve the energy production performance ofphotovoltaic array. The LMUs may include a solar module controller tocontrol the operation of the solar module, to monitor a status of thesolar module, and to link the solar module to the serial power bus forenergy delivery. The LMUs may also perform filtering and DC conversion,e.g., to buck or boost a module output voltage to a desired stringvoltage, of the power output by their respective solar modules to thestrings.

In some embodiments, the LMUs 104 a 1 through 104 mn may use the powerbus for sending data and communications. In some embodiments, the LMUsmay be connected to a separate communication network, either via wiresor wirelessly. In some embodiments, the LMUs may use the power bus andone or more of a wired or wireless network for sending data andcommunications. In some embodiments, an LMU may be configured to operatemore than one solar module. For example, an LMU could be configured tooperate each solar panel in a solar array, where each solar panelincluded two or more solar modules.

The LMUs 104 a 1 through 104 mn may be connected on one side to thesolar modules 102 a 1 through 102 mn in parallel, and on the other sidein series to strings 116 a through 116 m. The LMUs may receive differenttypes of input communications, for example, a requested duty cycle,which can be expressed as a percentage (e.g., from 0% to 100%) of timethe solar module is to be connected to the serial power bus, a phaseshift in degrees (e.g., from 0 degrees to 180 degrees), and a timing orsynchronization pulse. These inputs can be supplied, for example, asdiscrete signals, or can be supplied as data on a network, or compositesignals sent through the power lines 116 a to 116 m, or wirelessly, andin yet other cases, as a combination of any Rof these input types.

In some embodiments, the LMUs 104 a 1 through 104 mn may also monitor astatus of the solar modules 102 a 1 through 102 mn, for example, bymonitoring sensors which give operating parameters of the module such asvoltage, current, temperature, and the like. In some embodiments, theLMUs 104 a 1 through 104 mn may also monitor local meteorologicalconditions, for example, such as solar irradiance, air temperature, andthe like. The LMUs may be configured to optimize an operation of theirrespective solar module using the status of the solar module determinedby the monitoring.

In some embodiments, the LMUs can shut down the solar module based onone or more triggers determined by the monitoring, for example, anovervoltage, a high temperature, or the like, or based on an emergencyshutdown signal received from the controller 114. In some embodiments,the controller may output a system OK signal, and the LMUs shut downtheir respective solar module if the system OK signal is not receivedfor a predetermined period of time, for example, 10 seconds.

In some embodiments, the LMUs 104 a 1 through 104 mn may communicate thestatus of the solar modules 102 a 1 through 102 mn and localmeteorological conditions to a controller 114. The controller 114 maythen determine and generate the input communications for driving theLMUs, for example, a duty cycle, a phase shift, or a timing orsynchronization pulse, based at least in part on the statuses of thesolar modules and the meteorological conditions to optimize aperformance of the solar array.

In some embodiments, the controller 114 can cause the LMUs 104 a 1through 104 mn to shut down their respective solar module based on oneor more triggers determined by the monitoring, for example, anovervoltage, a high temperature, or the like, or based on an emergencyshutdown signal generated by and sent from the controller 114. Thecontroller 114 generates and sends the emergency shutdown signal, whichmay be based on an overvoltage in a combiner or an inverter, a conditionat connectors 112 a and 112 b, for example, to a mains power grid orlocal system, or an external factor, such as a fire alarm, seismicalarm, or the like. In some embodiments, the controller may generate andoutput a system OK signal, and the LMUs shut down their respective solarmodule automatically if the system OK signal is not received for apredetermined period of time, for example, 10 seconds.

The strings 116 a through 116 m are collected in combiner 108. Thecombiner 108 collects the DC power from the strings 116 a through 116 mand supplies DC power to a central inverter 110. The inverter 110 mayhave filters and capacitors on the input side. A capacitance of thecentral inverter 110 varies by application; however, in general, thereis a very large capacitance on the input side of an inverter in solarenergy applications. Even when the system is shutdown, for example, whena power grid to which the solar array is supplying energy is shutdown, aproblem remains that the capacitors on the input side of the centralinverter may still be holding a dangerous amount of charge.

The controller 114 may include a microcontroller or small single chipmicrocontroller (SCMC), for example, or may be implemented using anApplication-Specific Integrated Circuit (ASIC), Field-Programmable GateArray (FPGA), or other programmable logic. The controller 114 can evenbe implemented in discrete, functionally equivalent circuitry, or inother cases a combination of SCMC and discrete circuitry.

The controller 114 may be a stand-alone unit, or may be integrated withthe combiner 108, with the inverter 110, or with both the combiner andthe inverter into a single unit. In some embodiments, the controller 114is integrated with the inverter 100, monitors a performance of theinverter, determines and tracks a maximum power point, and controls theLMUs 104 a 1 through 104 mn based on, at least in part, the maximumpower point. Further, while depicted as a logical unit for purposes ofthis disclosure, the controller 114 may be a distributed device.

For example, the controller 114 could include maximum power pointtracking (MPPT) circuitry integrated with inverter 110, local controlcircuitry integrated with LMUs 104 a 1 through 104 mn or with theindividual solar modules 102 a 1 through 102 mn, and a stand-alonemicrocontroller unit (MCU) which communicates with and controls the MPPTand local circuit elements. The MPPT calculations by the MCU may beperformed, for example, using one or more known MPPT algorithms such asperturb-and-observe, incremental conductance, current sweep, or constantvoltage. The MPPT algorithms find the operating voltage that allows amaximum power output from the inverter. The controller 114 could alsoinclude multiple controllers, for example, with each controller beingresponsible for a string, or for one or more solar modules on a solarpanel.

The embodiment of FIG. 2 is a common arrangement of a photovoltaic solararray system, wherein the solar modules 102 a 1 through 102 mn supply DCpower to the strings 116 a through 116 m. The power is collected by thecombiner 108, and then supplied to the inverter 110. While this is onearrangement with which the teachings of the present disclosure may bepracticed, it is not the only such arrangement.

FIGS. 3A-3C are schematic structural diagrams illustrating differentinverter locations in photovoltaic arrays according to some non-limitingembodiments of the present disclosure. FIG. 3A is a schematic structuraldiagram of an arrangement similar to FIG. 2 , where DC converters 106convert the solar module output voltage to a desired string voltage. DCpower is carried by the strings to combiner 108, and there is a singlecentral inverter 110 for the solar array which outputs AC power toterminal 112. An implementation using a central inverter as in FIG. 3simple and reliable, but since it effectively treats the whole solararray as a single may not allow the best optimization of the solararray's output power by MPPT.

FIG. 3B is a schematic structural diagram of an arrangement where DCconverters 106 also convert the solar module output voltage to a desiredstring voltage, but there is a string inverter 110 on each string. Theoutputs of the string inverters 110 are then added in combiner 108 whichoutputs AC power from the solar array. String inverters represent amiddle ground between the simplicity of a single central inverter andthe ability to better optimize the solar array's output power bycontrolling the strings individually by MPPT.

FIG. 3C is a schematic structural diagram of an arrangement where DCconverters 106 convert the solar module output voltage to a desiredvoltage. There is a micro-inverter 110 connected between each DCconverter 106 output and its respective string. The AC power of thestrings is then added in combiner 108, which outputs AC power from thesolar array. Micro-inverters allow the greatest flexibility foroptimization of output power, but also require the most equipment.

The systems and methods disclosed below can be practiced in any of theconfigurations of FIGS. 2, 3A through 3C.

FIG. 4A is a schematic structural diagram illustrating a powerconverting system according to some embodiments of the presentdisclosure. The power converting system 200 includes a maximum powerpoint tracking (MPPT) controller 202, which is electrically coupledbetween at least one solar module and the input side of an inverter forthe solar array. The embodiment of FIG. 4 , as well as the otherembodiments of the photovoltaic system described hereinbelow, can beapplied to any of the solar array configurations of FIGS. 2, 3A through3C, or any other solar array configuration, as long as the photovoltaicsystem may be coupled between a solar module and an input side of aninverter having capacitive elements.

The MPPT controller 202 includes microcontroller unit (MCU) 204 and DCconverting circuitry 206. The MCU 204 may monitor the inverterperformance, perform MPPT calculations, control the DC convertingcircuitry 206, and may be programmed to perform some or all of thecalculations, control functions, and actions as described in thisdisclosure. The MCU 204 can be implemented in LMUs illustrated in FIG. 2or DC converters 106 illustrated in FIGS. 3A-3C to send and receivesignals from the controller 114, for example, via the strings orwireless communications, where the signals may include control signalssuch as emergency shutdown signals for the solar modules. In the powerconverting system 200 depicted as a unit in FIG. 4A, the DC convertingcircuitry 206 is electrically located between the at least one solarmodule and the respective inverter, while the MCU 204 can use the powerfrom the solar panel to control the operation of the convertingcircuitry, and perform communications and/or calculations. In someembodiments, one or more components of the MPPT controller may bedistributed throughout the solar array, with at least the DC convertingcircuitry being electrically located between the at least one solarmodule and the inverter.

The DC converting circuitry 206 includes an efficient switched modepower converter with synchronous, or active, rectification. The activerectification may be efficiently accomplished using transistors, forexample, MOSFETs, and synchronous switching in the DC convertingcircuitry 206 is controlled by the MCU 204. As shown in FIG. 4B, the DCconverting circuitry performing active rectification in a synchronousmode may transfer power from the solar panel to the inverter in oneforward mode, and from the inverter to the solar panel in a reversemode.

In FIG. 4A, during the operation of the converting circuitry 206, avoltage (Vrev_boost) at the “to solar panel” terminals connected to theat least one solar module is greater than a voltage (Vinverter) at the“to inverter” terminals connected to the string/inverter. Thus, the DCconverting circuitry 206 reduces, or “bucks,” the voltage (Vrev_boost)from the at least one solar module side down to the voltage (Vinverter)at the inverter side. From a different point of view, the convertingcircuitry 206 increases, or “boosts”, the voltage (Vinverter) at theinverter side to the voltage (Vrev_boost) to counter balance the voltage(Vpanel) from the solar panel. When the voltage (Vrev_boost) is lessthan the voltage (Vpanel), power flows from the solar panel to theinverter in the forward mode; and when the voltage (Vrev_boost) isgreater than the voltage (Vpanel), power flows to the solar panel fromthe inverter in the reverse mode.

In general, the DC converting circuitry 206 may include, for example, abuck converter, a buck-boost converter, or a auk converter. The DCconverting circuitry 206 can operate in a way that the voltage(Vinverter) at the “to inverter” terminals may nor may not be smallerthan the voltage (Vrev_boost) at the “to solar panel” terminals. For agiven voltage (Vinverter) at the inverter side, the converting circuitry206 can be controlled by MCU to either operate at a voltage (Vrev_boost)that is great than the voltage (Vpanel) from the solar panel and thus inthe reverse mode, or a voltage (Vrev_boost) that is less than thevoltage (Vpanel) from the solar panel and thus in the forward mode. Theadjustment can be effectuated by changing the voltage conversion ratio,for example, by adjusting the control parameters (e.g., duty cycle) usedby the MCU to control the converting circuitry.

For example, when the converting circuitry is a buck converterimplemented with a synchronous rectifier (e.g., as illustrated in FIG. 7), the MCU 204 can control the duty cycle and the frequency of thesynchronous switching operations in the DC converting circuitry 206 tochange the voltage conversion ratio and thus control the direction inwhich power flows across the DC converting circuitry 206. The MCU 204can control the DC converting circuitry 206 so that in a forward mode ofthe MPPT controller, the voltage on the solar panel is greater than thereverse boosted voltage from the DC converting circuitry 206. In theforward mode, power flows from the solar panel to the inverter. The MCU204 can also control the DC converting circuitry 206 so that in areverse mode of MPPT controller, the voltage on the solar panel is lessthan the reverse boosted voltage from the DC converting circuitry 206.In the reverse mode, power flows from the inverter to the solar panel,and is dissipated in the photodiodes of the at least one solar module.The DC converting circuitry 206 is software configurable, via the MCU204 adjusting the duty cycle and/or switching frequency of the DCconverting circuitry 206, to transition between the forward and reversemodes.

The system and method disclosed herein for synchronous rectification canbe designed for a distributed algorithm and, as such, needs to behave ina manner that reflects to the inverter the correct direction forcurrent, and thus power, to move. This behavior is achieved by having alow output impedance. This means that when voltage at the inverter sideis forced above a threshold voltage, for example, a threshold of aso-called “smart” voltage, Vsmart, which is typically set to 6% greaterthan maximum power point voltage, Vmp, the MPPT controllers are used totransfer the energy into the PV panels. The maximum power point voltage,Vmp, is determined by the MCU using an MPPT algorithm.

In other cases, when the inverter takes the string and/or array voltagedown (corresponding to different configurations from FIGS. 3A to 3C), oran overvoltage situation is detected, the photovoltaic system transfersthis power to the correct MPPT controllers for the PV panels todissipate, by running the elements as diodes in forward mode.

To achieve a synchronous operation of all connected MPPT controllers, anMPPT controller topology with both a forward and a reverse per pulsecurrent limit is utilized. In addition, during a rapid shutdown, wheninverter capacitors have to be discharged, the same mechanism asdescribed above may be used. At this stage, any input over thedisconnect voltage is increased by the MCU changing the MPPT controllerinto a boost converter. Normally, this phenomena happens at low power,so it does not justify another dedicated hardware-based circuit.

Optionally, the power converting system 200 connected to an inverter hasan MPPT function as part of the string supplying current to the inverterfrom the photovoltaic panels. Further, this MPPT controller may containa buck, or any other suitable topology, which when operated insynchronous mode can transfer energy from input to output or output toinput. The DC converting circuitry is typically for reducing the voltageof the panels, but the disclosure is not limited to this case only. Thephotovoltaic system also has an MCU for communication and executingcontrol programs controlling the buck converter, to enable the string tooperate at the MPPT point, as determined by an MPPT algorithm for thestring inverter. The buck converter is software-configurable, via theMCU, to operate as a reverse boost converter, enabling the system todraw energy out of the string and attached inverter and to dissipateenergy in the photodiodes of the PV panel.

In some embodiments, the controller 204 may, based upon certaintriggers, automatically change from operating the converting circuitryfrom the forward buck mode to the reverse boost mode to dissipate excessenergy in the photodiodes of the PV panel. These certain triggers may bean overvoltage condition (i.e., an overvoltage relative to Vsmart), anemergency shutdown signal, or the absence of a system OK signal.Further, the transition between reverse boost and forward buck mode mayoccur using a soft start approach, avoiding a surge current, or thetransition may occur on a pulse-by-pulse basis.

FIG. 5 is a schematic structural diagram illustrating a photovoltaicsystem 300 for connecting to an inverter according to some embodimentsof the present disclosure. The photovoltaic system 300 includes a solarpanel 310 having one or more solar modules and an MPPT controller 302.The MPPT controller 302 is configured to perform all the functions andis substantially similar to the MPPT controller 202 describedhereinabove. The MPPT controller 302 includes an MCU 304, DC convertingcircuitry 306, a disconnect 308, and filtering element 312. The MCU 304and the DC converting circuitry 306 perform the same functions and aresubstantially similar to the MCU 204 and the DC converting circuitry 206described hereinabove.

The filtering element 312 is disposed between the DC convertingcircuitry 306 and the inverter, or between the DC converting circuitry306 and a string to the inverter. The filtering element 312 isconfigured to smooth and stabilize an output voltage. The filteringelement 312 may include, for example, various combinations ofcapacitors, resistors, diodes, and the like, in series and in parallel.

The disconnect 308 is configured to disconnect the solar panel from theDC converting circuitry 306, and thus ultimately from the inverter. Thedisconnect 308 may include, for example, transistor switches, and may becontrolled via the MCU 304.

The MPPT controller 304 may, based upon certain triggers, automaticallychange from the forward buck mode to the reverse boost mode to dissipateexcess energy in the photodiodes of the PV panel. These certain triggersmay be an overvoltage condition (i.e., an overvoltage relative toVsmart), an emergency shutdown signal, or the absence of a system OKsignal. To effect the change between the forward and reverse modes, theMCU 304 controls the switching of the transistors, e.g., by changing theduty cycle and/or switching frequency.

The MCU 304 performs calculations for the operations which caneffectuate the reverse boosting mode, e.g., changing the duty cycle ofthe transistors (switch/rectifier pair) in the DC converting circuitryto increase the conversion ratio. The conversion ratio is the ratiobetween the input and output voltages. The required duty cycle to makethe conversion ratio such that the reverse boosted voltage is higherthan the panel voltage (which transitions the DC converting circuitry306 and MPPT controller 304 to the reverse mode) may be calculated fromthe known solar panel voltage and the current inverter side voltage. TheMCU 304 keeps increasing the conversion ratio (since the invertervoltage will keep dropping) until there is not sufficient power on theinverter side to sustain the reverse mode, i.e., until the power hasbeen dissipated from the input capacitor. After burning off the energyfrom the inverter side, MCU 304 may disconnect the solar panel 310 viathe disconnect 308 to complete the shutdown.

Further, the transition between reverse boost and forward buck mode mayoccur using a soft start approach, avoiding a surge current, or thetransition may occur on a pulse-by-pulse basis. The MPPT controller 304may also, for example, in the event of an emergency shutdown or absenceof a system OK signal, disconnect the solar panel 310 via the disconnect308 after the energy in the input capacitor has been dissipated in thephotodiodes of the solar panel 310.

FIG. 6 is a schematic structural diagram illustrating a photovoltaicsystem 400 for connecting to an inverter according to some embodimentsof the present disclosure. The photovoltaic system 400 is a distributedsystem.

The photovoltaic system 400 includes an MPPT controller 402, an MCU 404,converting circuitry 406, and a solar panel 410 having one or more solarmodules, which perform the same functions and are substantially similarto the MPPT controller 302, the MCU 304, the converting circuitry 306,and the solar panel 310 described hereinabove. The photovoltaic system400 also includes a disconnect 408 and a filtering element 412, whichperform the same functions and are substantially similar to thedisconnect 308 and the filtering element 312 described hereinabove.

Auxiliary preloading unit 416 is configured to create a power supply incases where the string is dead. It can also create power from the solarpanel 410. In some embodiments, power may be fed from the filteringelement 412.

The driver 418 provides power and level translation for switches in thedisconnect 408 and the DC converting circuitry 406. The driver 418 iscontrolled via discrete logic control circuitry 414 by the MCU 404,which does the fine tuning, logic, and also synchronization control ofthe MPPT controller 402, and other communications. Triggering signalsfor emergency shutdown or to change between the forward buck mode andthe reverse boost mode are generated by the MCU 404. The signals aresent to the driver 418 via the discrete logic control circuitry 414 toimplement the actions via switching elements in the disconnect 408 andthe DC converting circuitry 406 which are driven by the discrete logiccontrol circuitry 414.

FIG. 7 is a schematic structural diagram illustrating a photovoltaicsystem 500 for connecting to an inverter according to some embodimentsof the present disclosure.

The photovoltaic system 500 includes an MPPT controller 502, an MCU 504,and a solar panel 510 having one or more solar modules, which performthe same functions and are substantially similar to the MPPT controller402, the MCU 404, and the solar panel 410 described hereinabove. Thephotovoltaic system 500 also includes an auxiliary preloading unit 516,a driver 518, and discrete logic control circuitry 514 which perform thesame functions and are substantially similar to the auxiliary preloadingunit 416, a driver 418, and discrete logic control circuitry 414described hereinabove.

In the photovoltaic system 500, instead of the classic buck converterusing one switch and one rectifier, two transistors 520 and 522 are usedto enable synchronous rectification. Transistor 520 is the switch thatcharges an inductor 524. On release of transistor 520, transistor 522catches the flyback of 524 and pushes the current through filteringelement 512 to the inverter.

MOSFET transistors 532 and 534 are used to disconnect solar panel 510after an emergency shutdown. Multiple MOSFET transistors may be used inparallel as a disconnect, so that the power through any one MOSFET islimited. Also, the photovoltaic system 500 may include reverse currentdiodes 536, plus components (not shown) inside solar panel 510 whichare, essentially, for each component a diode in the forward direction.During an emergency shutdown, transistors 520 and 522 may be used as aboost converter, receiving the string voltage coming in at the inverterside through filtering element 512 and boosting that voltage into thesolar panel 510 such that the photodiodes of the solar panel 510 may beused to dissipate that energy. Such a process typically will not heatthe panel significantly or excessively, since panel efficiency in normaluse is about 15% and panels are normally absorbing large amount ofenergy and thus a short time energy boost has no effect and typicallywill not damage the diodes.

Typically, the process of absorbing the energy from the inverter'scapacitors will only last a short period of time, often only a fewseconds to boost the voltage sufficiently to empty the capacitors whenthe voltage is sufficient. A typical panel has an output voltage ofaround 40 volts, which is equivalent to about 72 solar cells. Operatedas diodes, they have a voltage drop of approximately 0.5 to 0.7 Volts,so a panel that has a nominal 40 Volt output would, at a voltage ofapproximately 40 to 50 Volts, consume the full power of the capacitors.As the transistors 520 and 522 are operated as a boost converter, withtransistor 520 acting as a switch and transistor 522 acting as arectifier, the current is reduced as the voltage is boosted. The solarmodules can discharge all together or one at a time. As a solar modulereaches 0 Volts, the switches at its output keep the output at 0 Volts,thus reducing the overall voltage in whole string accordingly. Thisapproach enables the system to distribute the energy of the capacitorsover most of the solar panels, thus discharging the capacitors veryquickly.

To avoid damage to any part of the system, in some cases typically thereverse operation is tightly monitored, also to allow inverter inputvoltage to not drop too fast, so the inverter can perform a gracefulgrid disconnect. Further, a so-called soft start is employed (meaning asurge or inrush current is avoided by gently throttling the change).Also, in some cases monitoring enables the system to change betweenreverse boost and forward buck mode on a pulse-by-pulse basis, tosupport balancing within a string or also between strings. Also, in yetother cases, there may be a preset power dissipation limit per panelthat may include additional information, including but not limited topanel and ambient temperature, sun irradiation, etc.

In some cases, a photovoltaic system connected to an inverter has anMPPT controller as part of the string supplying current to the inverterfrom the photovoltaic panels. Further, this MPPT controller contains abuck converter for reducing the voltage of the panels. It also has anMCU for communication and executing control programs, and controllingthe buck converter to enable the string to operate at the MPPT point.The buck converter is software-configurable to operate as a reverseboost converter, enabling the system to draw energy out of the stringand attached inverter and to dissipate energy in the photo diodes of thePV panel. In such cases, the controller may, based upon certaintriggers, automatically change from forward buck mode to reverse boostmode to dissipate excess energy. These certain triggers may be anovervoltage condition, an emergency shutdown signal, or the absence of asystem OK signal. Further, the change between reverse boost and forwardbuck mode may occur using a soft start approach, avoiding a surgecurrent, or it may occur on a pulse-by-pulse basis.

FIG. 8 is a schematic flowchart illustrating a process for transferringenergy between at least one photovoltaic module and an inverter havingan input capacitor according to some embodiments of the presentdisclosure. The method of FIG. 8 can be implemented in the system ofFIG. 5, 6 or 7 , using the power flow control technique as discussed inFIGS. 4A and 4B, for inverters connected in various configurations, suchas those illustrated in FIGS. 2 and 3A-3C.

A maximum power point tracking (MPPT) controller is coupled 600 betweenthe input capacitor of the inverter and the at least one photovoltaicmodule.

The MPPT controller includes a direct current (DC) converter configuredto reduce, in a forward buck mode, a voltage of the at least onephotovoltaic module, to supply power from the at least one photovoltaicmodule to the input capacitor of the inverter. The DC converter issoftware-configurable to increase, in a reverse boost mode, a voltage ofthe input capacitor of the inverter, to dissipate power from the inputcapacitor in the at least one photovoltaic module.

The MPPT controller also includes a micro control unit (MCU) configuredto control the DC converter to allow the at least one photovoltaicmodule to operate at a maximum power point. The MMPT controller may beconfigured according to any of the embodiments disclosed hereinabove.

The MCU drives the DC converter in the forward mode so that the voltageof the at least one photovoltaic module is bucked 602 via the DCconverter in the forward buck mode to supply power to the inputcapacitor of the inverter.

The MCU monitors 604 one or more triggers for an emergency shutdowncondition while the photovoltaic system is operating. The one or moretriggers may include, for example, at least one of an overvoltagecondition, an emergency shutdown signal, and an absence of a system OKsignal.

The MCU determines 606, as a result of the monitoring, whether a triggerfor an emergency shutdown condition has been met. If the MCU determinesthat an emergency shutdown trigger has been met, then the MCU continuesto change 608 the operation of the converter. If the MCU determines thatno emergency shutdown trigger has been met, then the MCU returns tomonitor 604 triggers.

Upon a determination 606 by the MCU from the monitoring 604 that anemergency shutdown condition has been met, the MCU reconfigures the DCconverter to change 608 from the forward buck mode to the reverse boostmode.

The MCU operates the DC converter in the reverse buck mode until theinput capacitor to the inverter has been discharged 610. The MCU thendisconnects 610 the solar module.

Various embodiments of the present disclosure may be implemented incomputer hardware, firmware, software, and/or combinations thereof.Methods of the present disclosure can be implemented via a computerprogram instructions stored on one or more non-transitorycomputer-readable storage devices for execution by a processor.Likewise, various processes (or portions thereof) of the presentdisclosure can be performed by a processor executing computer programinstructions. Embodiments of the present disclosure may be implementedvia one or more computer programs that are executable on a computersystem including at least one processor coupled to receive data andinstructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. Each computer program can be implemented in any suitable manner,including via a high-level procedural or object-oriented programminglanguage and/or via assembly or machine language. Systems of the presentdisclosure may include, by way of example, both general and specialpurpose microprocessors which may retrieve instructions and data to andfrom various types of volatile and/or non-volatile memory. Computersystems operating in conjunction with the embodiments of the presentdisclosure may include one or more mass storage devices for storing datafiles, which may include: magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and optical disks. Storagedevices suitable for tangibly embodying computer program instructionsand data (also called the “non-transitory computer-readable storagemedia”) include all forms of non-volatile memory, including by way ofexample semiconductor memory devices, such as EPROM, EEPROM, and flashmemory devices; magnetic disks such as internal hard disks and removabledisks; magneto-optical disks; and CD-ROM disks. Any of the foregoing canbe supplemented by, or incorporated in, ASICs (application-specificintegrated circuits) and other forms of hardware.

When solar modules are connected in series or mesh configuration, therecan be a problem in which weaker modules not only produce less energybut also affect other modules in the same string or wiring section. Bymeasuring one can determine that a few modules are weaker than theothers in most commercially installed strings. Thus, the string isgenerating less power than the sum available at each module if moduleswere operated separately.

At least one embodiment of the present disclosure provides methods andsystems to switch on and off weak modules in the string in a way thatthe current on the string bus from the good modules won't be affected bythe weak modules.

The present invention allows transmission of data from solar modules toa central (or system controller management) unit and other localmanagement units in an energy production or photovoltaic system withoutadding significant cost. One embodiment of the present inventioninvolves using the typically undesired electrical noise produced whenoperating local management units (sometimes referred to as “controllers”or “converters”) to act as a carrier system for data to be transferred.As there are a multitude of solar modules, each can be run on a slightlydifferent frequency. Such an approach allows a receiver in the energyproduction or photovoltaic system to identify the carrier signal of eachlocal management unit separately. This approach has the added benefit ofreducing the overall system noise, because each local management unitsends “noise energy” in a different part of the spectrum, thus helpingto avoid peaks.

While certain embodiments have been described herein, these embodimentsare presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, using the teachings in this disclosure,a person of ordinary skill in the art could modify and adapt thedisclosure in various ways, making omissions, substitutions, and changesin the form of the embodiments described herein without departing fromthe spirit of the disclosure. The accompanying claims are intended tocover such forms or modifications as would fall within the scope andspirit of the disclosure.

What is claimed is:
 1. A photovoltaic system for connecting to aninverter, the photovoltaic system comprising: at least one photovoltaicmodule; and a controller coupled between the inverter and the at leastone photovoltaic module, wherein the controller includes: a converterconfigured to reduce, in a forward buck mode, a voltage of the at leastone photovoltaic module, to supply power from the at least onephotovoltaic module to the inverter; and a microcontroller unit (MCU)configured to control the converter to allow the at least onephotovoltaic module to operate at a maximum power point, wherein thecontroller is configured to change from the forward buck mode to areverse boost mode using a soft-start approach to avoid a surge current.2. The photovoltaic system of claim 1, wherein a trigger of one or moretriggers is an overvoltage condition.
 3. The photovoltaic system ofclaim 1, wherein a trigger of one or more triggers is an emergencyshutdown signal.
 4. The photovoltaic system of claim 1, wherein atrigger of one or more triggers is the absence of a system OK signal. 5.The photovoltaic system of claim 1, wherein the controller is furtherconfigured to change the buck converter from the forward buck mode tothe reverse boost mode using a soft-start approach to avoid a surgecurrent.
 6. The photovoltaic system of claim 1, wherein the controlleris further configured to change between the reverse boost mode and theforward buck mode occurs on a pulse-by-pulse basis.
 7. The photovoltaicsystem of claim 1, wherein the controller is disposed with the inverter,and wherein the inverter is one of a central inverter, a stringinverter, and a micro-inverter in photovoltaic array including one ormore strings of photovoltaic modules.
 8. The photovoltaic system ofclaim 1, further comprising: an emergency shutdown disconnect configuredto electrically disconnect the at least one photovoltaic module from thephotovoltaic system, wherein the emergency shutdown disconnect comprisesone or more metal-oxide semiconductor field-effect transistors(MOSFETs).
 9. The photovoltaic system of claim 1, wherein the controlleris further configured with a preset power dissipation limit for the atleast one photovoltaic module.
 10. The photovoltaic system of claim 9,wherein the preset power dissipation limit is based on at least one of aphotovoltaic module temperature, an ambient temperature, and a solarirradiance.
 11. The photovoltaic system of claim 1, wherein theconverter includes at least one of a buck converter, a buck-boostconverter, and a auk converter.
 12. A photovoltaic system for connectingat least one photovoltaic module to an inverter, the photovoltaic systemcomprising: a controller coupled between the inverter and the at leastone photovoltaic module, wherein the controller includes: a converterconfigured to reduce, in a forward buck mode, a voltage of at least onephotovoltaic module, to supply power from the at least one photovoltaicmodule to the inverter; and a microcontroller unit (MCU) configured tocontrol the converter to allow the at least one photovoltaic module tooperate at a maximum power point, wherein the controller is configuredto, based upon one or more triggers, automatically change the converterfrom the forward buck mode to a reverse boost mode to dissipate excessenergy.
 13. The photovoltaic system of claim 12, wherein a trigger ofthe one or more triggers is an overvoltage condition.
 14. Thephotovoltaic system of claim 12, wherein a trigger of the one or moretriggers is an emergency shutdown signal.
 15. The photovoltaic system ofclaim 12, wherein a trigger of the one or more triggers is the absenceof a system OK signal.
 16. The photovoltaic system of claim 12, whereinthe controller is further configured to change the converter from theforward buck mode to the reverse boost mode using a soft-start approachto avoid a surge current.
 17. The photovoltaic system of claim 12,wherein the converter includes at least one of a buck converter, abuck/boost converter, and a auk converter.
 18. The photovoltaic systemof claim 12, wherein the controller is disposed with the inverter, andwherein the inverter is one of a central inverter, a string inverter,and a micro-inverter in photovoltaic array including one or more stringsof photovoltaic modules.
 19. A method for transferring energy between atleast one photovoltaic module and an inverter, the method comprising:coupling a controller between the inverter and the at least onephotovoltaic module, wherein the controller includes: a converterconfigured to reduce, in a forward buck mode, a voltage of the at leastone photovoltaic module, to supply power from the at least onephotovoltaic module to the inverter; and a microcontroller unit (MCU)configured to control the converter to allow the at least onephotovoltaic module to operate at a maximum power point, bucking, ascontrolled by the MCU, the voltage of the at least one photovoltaicmodule to the inverter via the converter in the forward buck mode tosupply power to the inverter; monitoring, by the MCU, one or moretriggers for an emergency shutdown condition; and changing, ascontrolled by the MCU, upon a determination by the MCU from themonitoring that an emergency shutdown condition has been met, theconverter from the forward buck mode to a reverse boost mode.
 20. Themethod of claim 19, wherein the one or more triggers include at leastone of an overvoltage condition, an emergency shutdown signal, and anabsence of a system OK signal.